1. Field of the Invention
The present invention relates to apparatus for feeding stock material to press and, more particularly, to apparatus for feeding stock material by moving a slide block feed through a preselected distance.
2. Description of the Prior Art
It is the conventional practice in high speed automatic press operations to feed a preselected length of stock material from a coil to the dies of the press for punching, stamping, cutting or the like. The strip of stock material must be fed from the coil in timed relation with the press operation. The stock material is moved into a position between the dies by the feeding apparatus. After the press operation is completed, the feeding apparatus is actuated to advance another length of stock material to the press. The feeding of the stock material to the press must be coordinated with each press operation so that, prior to each operation, a new segment of stock material is moved into position relative to the dies of the press.
Typically, a high speed feeding apparatus for a power punch press utilizes feed rolls for feeding the stock. U.S. Pat. Nos. 4,133,216 and 4,138,913 are examples of one type of feeding apparatus in which the feed rolls are drivingly connected by a plurality of meshing gears to an input shaft which is drivingly connected to the punch press crankshaft. A drive utilizing a specific arrangement of cams and gears receives continuous, uniform rotation from the input shaft and converts the rotation to a noncontinuous step-by-step, intermittent rotational movement of the driven feed roll. With this arrangement, the feed rolls advance intermittently through a 360.degree. rotational cycle. During the single dwell period of the rotational cycle, the driven feed roll is not rotated and the punching operation is carried out. After the punching operation is completed, the feed rolls are again incrementally advanced so that another preselected length of stock material is passed through the press.
U.S. Pat. Nos. 3,758,011 and 3,784,075 are examples of another type of incremental feed apparatus that converts continuous rotation of a drive shaft to contrarotating movement of the feed rolls. The drive shaft is connected through a pair of meshing gears to a level that is oscillated to and fro. The pivotal movement of the lever is transmitted to a shaft that is, in turn, coupled to the feed rolls. The oscillatory movement of the lever and shaft is transmitted to the feed rolls to generate contrarotating movement. The feed length can be changed by altering the amplitude of the contrarotating movement of the feed rolls. Synchronously with the contrarotating movement, the feed rolls move toward one another into a feed position and move away from one another into an idling position. These apparatus, however, require a complex arrangement for interconnecting the operations of feeding, clamping and releasing the feed rolls, which requires many component parts and necessitates increased maintenance and replacement of worn parts.
U.S. Pat. No. 4,316,569 provides an apparatus for intermittently feeding a work piece or stock material to a punch press by converting continuous rotation of a cam surface to oscillating rotational movement of a cam follower, which is transmitted through an adjustable linkage to advance the driven feed roll in contact with the stock material through a preselected angle of rotation corresponding to a preselected feed length. The feed length is adjustable by changing the length of travel of the linkage mechanism. The driven feed roll rotates from an initial position through a preselected angle in a first direction to feed a selected length of material, remains stationary during a first dwell period and is released from the material, rotates in the opposite direction back to its initial feed position, remains stationary for a second dwell period and engages the material for another feed cycle. The intermittent feeding operation is coordinated with the operations of feed roll release and stock material clamping.
All of these prior art feeding devices utilize feed rolls to move the stock material from a coil to the dies of a press. A problem arises, however, with using feed rolls when the stock being fed is a small wire or bar. With flat stock, the feed rolls engage the stock along a line of contact with the pressure typically being distributed evenly across the entire line. When wire stock or small bar stock is fed, however, there is usually only one point of contact between the stock and the feed rolls. As a result, the pressure applied to the feed rolls tends to distort the shape of the wire or bar and can even extrude it. Since the length of stock material fed depends on the circumference of the feed roll, any distortion or extrusion of the wire or bar caused by the pressure of the feed rolls results in an inaccurate length of material being fed to the press. Of course, if less pressure is used, the feed rolls cannot grip the stock material sufficiently to advance it. Thus, there is a need for a press feeding mechanism which overcomes this distortion problem while at the same time being easily adjustable.
Sliding block press feeds are known in the art. A standard sliding block press feed operates by gripping the stock material and moving it forward into the press. When the sliding block reaches a stop block or the end of its mechanical linkage, the stock material is simultaneously released and the sliding block is returned for the next feeding cycle. Typically, these sliding block press feeds are operated in a timed sequence, with the sliding block timed to release the stock at the instant it reaches the stop block or the end of its mechanical linkage. Unless the timing is perfect, there will be error in determining the feed length since a premature or late release of the stock will result in the wrong feed length being fed to the press. Thus, there is a need for precisely controlling and rapidly changing the predetermined lengths of stock material fed to a press by a sliding block feed.